The invention relates to an apparatus for treating water by means of an electric field. The apparatus has a treatment chamber. An anode and a cathode is arranged in this treatment chamber. When a preferably inhomogeneous electric field is applied between the anode and the cathode, seed crystals of minerals contained in the water are formed on the cathode. These seed crystals are separated from the cathode by stripping means and carried away with the flowing water.
Drinking water contains essential minerals, among others calcium and magnesium carbonates. Such minerals, in total, are called water hardness. On one hand, such minerals are important under health aspects. On the other hand, they may cause malfunction of the drinking water installation, in particular if the water is heated. When the water is heated in a drinking water heater, for example, insoluble lime depositions, also called boiler scale, are formed. This boiler scale is formed on the warm side of the installation. Boiler scale impedes heat transmission. In tubes, the boiler scale, over the years, may result in closure of the tube installation downstream of the drinking water heater.
In order to avoid such depositions of boiler scale, the drinking water has been xe2x80x9csoftenedxe2x80x9d. This softening process removes the minerals from the drinking water. Such softening can be achieved by ion exchange or reverse osmosis. This avoids the formation of boiler scale. In exchange therefor, however, the quality of the drinking water is reduced by the removal of the minerals, which, for other reasons, are desirable.
Methods of treating drinking water by means of a so-called xe2x80x9celectro-physicalxe2x80x9d apparatus is known. Such electro-physical apparatus causes the formation of seed crystals in the drinking water. The seed crystals are carried away by the drinking water. The conglomeration of the seed crystals results in the drinking water thus treated causing less deposition in the form of boiler scale, on one hand. On the other hand the minerals in the drinking water are retained.
The treatment by means of electro-physical apparatus is substantially based on the following principle:
Drinking water always contains a certain proportion of carbon dioxide (CO2) dissolved therein. This carbon dioxide forms a reaction equilibrium with the remaining components, calcium hydrogen carbonate (Ca(HCO3)2 being formed from CaCO3 in accordance with the reaction equation
CaCO3+H2O+CO2⇄Ca(HCO3)2
If the water is heated, CO2 will escape from the water and boiler scale will be formed. It is, however, also possible to change purposefully the lime-carbon dioxide equilibrium in the drinking water.
If carbon dioxide is supplied to the water, this will result in shifting the equilibrium to the left in the above equation. Seed crystals of calcium carbonate (lime over-saturation) are formed from the calcium hydrogen carbonate present in the water. Then the subsequently formed calcium carbonate will be deposited predominantly on the once generated seed crystals, i.e. the seed crystals xe2x80x9cgrowxe2x80x9d.
This reaction is caused electrolytically in a treatment chamber containing a cathode and an anode. The seed crystals are formed on the cathode. The seed crystals have to be added to the drinking water after they have grown sufficiently. Then carbonate is already present in the form of seed crystals in the drinking water, when the drinking water is heated. There is no need of generating seed crystals anew. Accordingly, the carbonate will be deposited predominantly on the seed crystals carried away in the water rather than on the installation elements.
It has been found that development of seed crystals is improved if the electric field between the cathode and the anode is inhomogeneous.
EP patent application 0,751,096 discloses an apparatus for the electro-physical drinking water treatment by means of an electric field wherein an electric field inhomogeneous in space is generated by an a.c. voltage superimposed to a d.c. voltage.
A further prior art apparatus comprises a special steel brush serving as the cathode on which seed crystals are formed. These seed crystals are separated from the cathode by means of a stripper. This stripper is a comb which is passed through the special steel brush an and causes deformation of the flexible xe2x80x9cbristlesxe2x80x9d.
It is an object of the invention, to provide an improved apparatus for the electro-physical treatment of drinking water.
It is a further object of the invention, to provide an apparatus for the electro-physical treatment of drinking water which is of simple and inexpensive design.
It is a still further object of the invention to provide an apparatus for the electro-physical treatment of drinking water which has high efficiency with regard to the formation of seed crystals.
It is another object of the invention to provide an apparatus for the electro-physical treatment of drinking water wherein the cathode is kept permanently free from lime depositions.
In order to achieve these and other objects, an apparatus for treating water by means of an electric field has a treatment chamber. An anode and a cathode is arranged in this treatment chamber. The cathode has a plurality of parallel elongated elements. Removing means are provided for removing, from these elongated elements of the cathode, seed crystals formed thereon of minerals contained in the water. These removing means comprise a perforated disc, the elongated members of the cathode extending through the holes of the perforated disc. Such perforated disc permits safe removal or separation of the seed crystals from the elongated elements.
The elongated elements may be rigid pins.
Narrow fit between the pins and the holes of the perforated disc for stripping the seed crystals may result in friction, whereby a rather large force is required to axially displace the perforated disc. In order to avoid this friction, the pins of the cathode may extend in the flow direction of the water, the holes of the perforated disc having a larger diameter than the pins and defining flow passage restricting means for increasing the flow velocity of the water at the surface of the pins. To this end, the holes in the perforated disc through which the pins of the cathode extend may be nozzle-shaped, the smaller diameter of the nozzle being downstream.
The perforated disc is movable in the flow direction over the lengths of the pins. As long as the pins of the cathode extend through the perforated disc, there is a reduced flow passage, which causes increased flow velocity. Thereby, seed crystals adhering to the cathode are flushed away and are added to the drinking water. Thanks to the nozzle-shaped or conical holes, continuous reduction of the flow passage and increase of the flow velocity is achieved.
In the absence of water flow, the perforated disc may be held, by means of a spring, in a position in which the pins extend through the holes of the perforated disc with their full lengths. When water flows, the perforated disc is displaced by the water pressure against the force of the spring and is shifted over the pins of the cathode. Then the seed crystals are removed each time, when water flow is initiated by tapping of water, for example.
In order to avoid restriction of the normal water flow through the perforated disc and the pins, the perforated disc may be displaced by the water pressure beyond the lengths of the pins. In this way, heavy restriction of the water flow takes place only during an initial phase of the tapping procedure.
In another embodiment of the invention, the seed crystals are removed by stripping means, which are movable over the surface and driven by an electric drive motor, and are taken along by the water flow. A shut-off valve governing the water flow is provided in a fitting part of the apparatus. Furthermore, monitoring means are provided for monitoring, in accordance with given safety criteria, the water quantity flowing through the apparatus, in order to avoid damages caused, for example, by leaking water. The shut-off valve and the drive motor are also under the control of the monitoring means to close the shut-off valve, when the monitoring means respond.
In this embodiment, motor-driven stripping means are guided over the cathode. The stripping means need not be moved by the water pressure. Thereby, there is no restriction of the water flow. Larger forces can be exerted by the drive motor. The servo or drive motor required therefor is, simultaneously, used for the closing of the shut-off valve in the water pipe, if, for example, unusually high water flow is detected in the case of a burst in a water pipe, or, for example, water is flowing over an unusually long time indicating inadvertent leaving open of a water tap. Therefore, different functions can be fulfilled with one apparatus and one servo or drive motor used for different purposes.
The perforated disc may be moved against the action of a return spring through a transmission comprising a cam driven by the servo or drive motor and a push rod.
Using a servo or drive motor for moving the perforated disc permits passing the water flow between the pins and transverse to the pins.
Embodiments of the inventions will be described hereinbelow with reference to the accompanying drawings.